Low leakage plunger assembly for a high pressure fluid system

Abstract

A fluid control device for use in a high pressure fluid system, the device including a device body with a cavity and a high pressure circuit, a plunger positioned for reciprocal movement in the cavity, and a leakage reduction cap mounted to the plunger for reducing fluid leakage flow. In one implementation, the leakage reduction cap includes a flexible portion positioned between the device body and the plunger, and defining an annular clearance gap between the leakage reduction cap and the device body. The flexible portion of the leakage reduction cap resiliently flexes radially outwardly in response to fluid pressure forces to reduce the annular clearance gap so as to minimize fluid leakage flow through the annular clearance gap.

Description

[0001]This application claims priority to U.S. Provision application No. 60 / 907,035, filed Mar. 16, 2007BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]This invention relates to a plunger and barrel assembly for a fluid system which effectively minimizes leakage through a clearance between the plunger and the barrel assembly.[0004]2. Description of the Related Art[0005]Engine designers are continually seeking improvements in engine design which improve engine efficiency. One manner of improving engine efficiency is to improve the operational efficiency of the fuel system. Specifically, any leakage of high pressure fuel within the fuel system represents wasted energy that can reduce engine efficiency. Loss of high pressure fuel has recently become an even greater problem as injection pressure levels are increased in an effort to improve fuel economy and reduce emissions as required by recent and upcoming legislation.[0006]Undesirable leakage of fuel often occurs in a ...

AI Technical Summary

Benefits of technology

[0013]One advantage of the present invention, therefore, is in providing an improved fluid control device capable of optimally minimizing fuel leakage between the plunger and the barrel, thus increasing efficiency.

[0014]Another advantage of the present invention is in providing an improved fluid control device which can be applied to either a valve or a pump to effectively reduce fluid leakage between the pump or valve member and its body forming a bore.

[0015]Yet another advantage of the present invention is in providing an improved fluid control device which can be applied to fuel pumps, including unit fuel injectors and reciprocating plunger type pumps positioned upstream from a fuel injector in a high pressure fuel system.

[0016]Another advantage of the present invention is in providing such an improved fluid control device which does not require increasing the package size of the device in which the fluid control device is applied.

[0017]Still another advantage of the present invention is in providing an improved fluid control device which causes the operating clearance between the plunger and barrel to decrease as fuel pressure increases.

[0018]Another advantage of the present invention is in providing an improved fluid control device including a leakage reduction cap which permits the material for the cap to be selected independently from the barrel to better meet lubricating and structural requirements for the components.

Problems solved by technology

Specifically, any leakage of high pressure fuel within the fuel system represents wasted energy that can reduce engine efficiency.

Loss of high pressure fuel has recently become an even greater problem as injection pressure levels are increased in an effort to improve fuel economy and reduce emissions as required by recent and upcoming legislation.

However, the practice of requiring closer tolerances increases manufacturing costs.

However, this method undesirably increases the size and weight of the components and, thus, the fuel system.

However, these references do not suggest reducing the leakage between the plunger and adjacent bore wall and, therefore, are subject to the disadvantages discussed hereinabove.

Although deformation of the integral portion tends to close the clearance gap to reduce leakage, the resulting close tolerances may result in increased wear, or possibly scuffing, of the valve body or piston resulting, over time, in excessive clearances.

For the Kabai et al. design, excessive wear would eventually require replacement of the entire piston and / or valve body, unnecessarily increasing costs.

Also, the integral portion disadvantageously provides reduction in the pressure gradient over only a limited, localized portion of the seal length and thus fails to minimize leakage in an optimum manner.

In addition, the integral portion is formed by machining internal passages into the valve body or piston undesirably increasing manufacturing time and costs.

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